5 Unicast, Broadcast, Multicast, Anycast Unicast: One specific receiver Broadcast: Many receivers, all on the network Multicast: Many receivers, all of a specific group Anycast: One receiver, "nearest" of a specific group Geocast: Many receivers, all of a geographic region Pictures: Wikipedia 5

6 Bandwidth Economy Fully heterogeneous individual requests: Required bandwidth = stream bandwidth x number requests Homogeneity of request helps saving bandwidth: Same content for many clients, but different playback times:» Broadcast with caching Same content at same time for many clients» Multicast (splitting streams) Pre-planning saves bandwidth (Individual) transmission of pre-booked content in non-real time ( download and play ) 6

7 Streaming, Streaming Media Streaming media means real-time delivery of moving images, moving text and sound, from a server to client (over the Internet). Delivery types for audio and video content: Download and Play: Content must be downloaded completely to the client before it can be played Progressive Download: Playback is started while download is still in progress. Download rate independent of program bit rate. True Streaming: Delivered media is viewed/listened in real-time.» Playback takes place with roughly the same rate as delivery of data» Delay between send and receive event of data packet kept small Subtypes of True Streaming: Static File Streaming: Delivery of pre-recorded media files. Often also called on-demand delivery (e.g. Video on Demand) Live Streaming Based on material from 7

8 Session A session is an association between communicating parties, which Persists over a limited time span Incorporates at least two parties May comprise a large number of communication connections of different characteristics Examples of sessions: Movie streamed to consumer, consisting of audio and video parts Multimedia conference among five participants, consisting of audio and video source from each of of the participants (plus possibly some global information) Session awareness at which levels? At application level: unavoidable At network level: possible» Requires specific protocols 8

15 IP and TCP Internet Protocol Network communication protocol (ISO layer 3) Packets transferred from address to address (through routers) Main problems:» Variable network latency» Packet order on arrival may be different than on sending» Packets may be lost Transport Control Protocol (TCP) Connection establishment (by three-way handshake )» Connections are sequences of associated IP packets Sequencing of bytes with forwarding acknowledgement number Non-acknowledged bytes are re-transmitted after a defined time period Flow control For audio/video streaming: Retransmissions (and associated delays) are harmful Lost packets can be tolerated to some extent 15

17 Real-Time Transport Protocol RTP Transport protocol specifically developed for streaming data IETF (Internet Engineering Task Force) RFC (Request for Comments) 1889 RTP usually carried over UDP and used for push model mainly Very important: RTP does not at all change the way how IP packets are transferred in the network! To achieve Quality of Service, additional network technologies are required (see above) RTP used (mainly historically) by: Apple QuickTime architecture RealSystems streaming architecture Modern Internet structure does no longer support RTP at many places in particular, in Content Delivery Networks, see later 17

22 Real-Time Control Protocol RTCP RTCP controls the transmission (not the setup of connection) RTCP periodically sends monitoring information to all participants in a streaming session Main functions of RTCP: Feedback on QoS of transmission» Information for adaptive codecs, e.g. whether problem is local or global Identification of sender by canonical name» Helpful when synchronization source changes» Supports lip synchronization between audio and video Number of participants in a session» Adaptation of sending rate of RTCP control information to number of participants, to avoid network overload Transmission of additional information, e.g. names of session participants 22

41 Key Problems in CDNs Replica placement: Where to place copies of web sites or other content Problem is in general NP-hard (Karlsson, Karamolis, 2004) Replica placement algorithms (RPA) achieve a suboptimal solution within reasonable time frame Global information is difficult or costly to get - RPA uses local information mostly CDN providers typically try to observe global network performance to some extent Request routing: Mechanism and policy of redirecting client requests to a suitable server containing the requested content Redirection algorithm: Decides what node to direct a client request to Redirection mechanism: Way of redirecting the request (client, network) 41

45 Usage of Video Streaming Comscore.com: EU-3 = Germany, France, UK U.S. Internet users watched 39 billion online content videos in September 2012; The total number of unique viewers was million; This represents 85 percent of U.S. Internet users; Forrester Research, November 2012: Video is the fastest-growing digital content category; we forecast that more than 90% of the online population will regularly watch online video by Online video audience penetrations will rise significantly as video on demand, pay per view, and catchup TV become mainstream. And with pay- TV penetrations in the EU-7 nations considerably lower than in the US, there s more scope for paid online video to grow. Source: 45

49 What is a Media Streaming Player? Still in 2011, main meaning was: Software for PCs and mobile devices Google search in 2013, main hits: Apple TV, Roku XD, D-Link MovieNite, WD TV Live, etc. Multimedia Research Group (MRG): In 2011, worldwide unit shipments of streaming media players grew to 6.8 million units. However, demand for these products continues to increase steadily and MRG in projecting that total unit shipments will exceed 8.3 million in Despite market challenges, demand projected to remain healthy through new-high-for-streaming-media-players/ cepro.com 49

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